A so-called spectrophotometer is commonly known, which is configured to irradiate a sample with white light and measure an amount of transmitted light, to thereby measure absorbance of the sample for each wavelength. The spectrophotometer detects a component in the sample by utilizing that the absorbance of the sample differs depending on the concentration of a light-absorbing substance in the sample.
For example, Patent Literature 1 discloses a spectrophotometer to be used for inspection of fruit or vegetables and the like, which is capable of measuring even such an object to be measured that transmits light in an amount greatly different depending on the density and size even in the same kind of fruit or vegetables. Specifically, Patent Literature 1 discloses a spectrophotometer including two light receiving units, that is, a main light receiving unit and a sample light receiving unit, an amplifier, an AD converter, and others. First, a value acquired from the sample light receiving unit and a reference value set in advance are compared with each other, and the gain of an amplifier circuit is appropriately adjusted in accordance with the result of comparison. After that, a value acquired from the main light receiving unit is read as digital data.